This invention relates generally to rotary cone drill bits and, more particularly, to a rotary cone drill bit having at least one cutter cone assembly with a machined cutting structure and method of forming the cutting structure.
A wide variety of rotary cone drill bits are used for drilling earth boreholes for the exploration and production of oil and gas and for mining operations. Such drill bits often employ multiple rolling cutter cone assemblies, also known as rotary cutter cone assemblies. The cutter cone assemblies are typically mounted on respective spindles or journals that extend downwardly and inwardly relative to an axis extending through an associated bit body so that conical surfaces of the cutter cone assemblies tend to roll on the bottom of a borehole in contact with the adjacent earth formation. Cutter cone assemblies generally have circumferential rows of milled teeth or inserts to scrape, cut and/or gouge the formation at the bottom of the borehole. Forming teeth on a generally conically shaped forging by milling is often a relatively expensive, time consuming process. Multiple milling steps are frequently required to form each tooth of a typical milled teeth cutting structure.
Milled teeth on conventional cone assemblies tend to wear in those areas that engage the bottom and side wall of a borehole during drilling operations. Milled teeth typically have a generally pyramidal configuration with a trapezoidal cross-section extending from the exterior surface of the associated cutter cone assembly. The generally pyramidal configuration is formed during the milling operation to provide sufficient structural support with adjacent portions of the associated cutter cone assembly. As a result of slanted surfaces associated with the generally pyramidal, milled teeth will generally become more blunt from abrasion, erosion and wear during drilling operations. Unless additional weight is applied to the associated rotary cone drill bit, the penetration rate will generally decrease as the area of contact increases with the bottom of a borehole resulting from the wear of milled teeth having a generally pyramidal configuration.
The service life of a rotary cone drill bit having cutter cone assemblies with respective milled teeth cutting structures may be improved by the addition of abrasion and wear resistant materials to selected wear areas of each tooth. The addition of abrasion and wear resistant materials to milled teeth is sometimes referred to as xe2x80x9chardfacing.xe2x80x9d In a hardfacing operation, abrasion and wear resistant material is applied to the teeth to provide not only a wear resistant surface to reduce the rate at which each milled tooth is worn off, but also to maintain sharper cutting edges as the teeth wear.
Examples of rotary cone drill bits having cutter cone assemblies with respective milled teeth cutting structures are shown in U.S. Pat. No. 5,579,856 entitled Gage Surface and Method for Milled Tooth Cutting Structure and U.S. Pat. No. 2,533,256 entitled Drill Cutter. Such drill bits may sometimes be referred to as xe2x80x9csteel toothxe2x80x9d drill bits or xe2x80x9cmilled toothxe2x80x9d drill bits.
Conventional cutter cone assemblies with milled teeth often include multiple rows of teeth disposed on the respective conical surfaces. Such cutter cone assemblies somewhat resemble spur gears or bevel gears with interlocking or intermeshing teeth. Variations of these patterns include skewing the teeth similar to that of a spiral bevel gear, or even an alternating skew to produce a herringbone effect. Another accepted version of a drill bit is an interrupted circumferential disc having a resulting appearance of teeth aligned end to end around the periphery of the associated cutter cone assembly.
In accordance with teachings of the present invention, disadvantages and problems associated with previous rotary cone bits having multiple cutter cone assemblies with milled teeth cutting structures have been substantially reduced or eliminated. One aspect of the present invention includes providing a rotary cone drill bit having at least one cutter cone assembly with a machined cutting structure formed by a series of lathe turns and/or plunge cuts. The desired machined cutting structure may be integrally formed on a forging or casting have a generally conical configuration associated with cutter cone assemblies.
For one application, the machined cutting structure may be described as a series of corrugated webs having a generally sinusoidal configuration. Each corrugated web preferably extends circumferentially around the conical surface of an associated cutter cone assembly. The corrugated webs on each cutter cone assembly are spaced a selected distance from each other to provide an intermeshing or overlapping relationship with corresponding corrugated webs found on adjacent cutter cone assemblies. Depending upon anticipated downhole drilling conditions, the machined cutting structure may be heat treated or covered with a layer of hardfacing material using presently available techniques and materials or any future techniques and materials developed for rotary cone drill bits.
For another application, the machine cutting structure may be described as a series of interrupted webs formed by cutting or machining a generally continuous corrugated web into individual cutting elements extending from the exterior surface of an associated cutter cone assembly. The interrupted webs on each cutter cone assembly and respective individual cutting elements of each interrupted web are preferably spaced a selected distance from each other to provide an intermeshing or overlapping relationship with corresponding interrupted webs and cutting elements formed on adjacent cutter cone assemblies. The present invention allows optimizing the resulting machined cutting structure to provide substantially enhanced downhole drilling action.
Technical advantages of the present invention include the ability to use a wide variety of metal shaping and/or machining operations to form a cutting structure on the exterior of a cutter cone assembly with aggressive cutting element profiles. As cutter cone assemblies with selected machined cutting structures are rolled over the bottom of a borehole, each cutting element will preferably first attack the downhole formation with a slicing type effect, then translate into a crosscut and plowing type effect. This combination of drilling actions will enhance penetration rates, as well as improved bottom hole cleaning. Machined cutting structures may be formed on cutter cone assemblies in accordance with teachings of the present invention to provide for more favorable drill bit geometry to improve directional drilling control. The resulting machined cutting structures provide increased circumferential surface engagement with the formation at the bottom of a borehole which improves dynamic stability and reduces gauge wear without any reduction in downhole drilling efficiency.
Many different lathe turning steps, plunge cutting steps and/or other metal machining techniques may be used in accordance with teachings of the present invention to form machined cutting structures with a wide variety of geometric configurations and selected cutting profiles for each cutting element. The present invention is not limited to any specific sequence of machining operations, cutting element profiles, corrugated web configuration and/or interrupted web configurations. The present invention also allows using a wide variety of metals, metal alloys and other materials to form each cutter cone assembly.
Further, technical advantages of the present invention include providing a rotary cone drill bit with at least two and preferably three cutter cone assemblies having machined cutting structures. The geometric configuration and cutting profile of each cutting element may be optimized to improve overall downhole drilling efficiency of the associated drill bit. Each cutting element is preferably formed with a generally uniform thickness and steep sides extending generally perpendicular from the exterior surface of an associated cutter assembly. The cutting profile of each cutting element will remain relatively sharp despite substantial abrasion and wear of the associated cutting element. An aggressive cutting profile may be formed on each cutting element to allow increasing the penetration rate of the associated drill bit, while at the same time extending downhole service life since the cutting elements will remain relatively sharp despite abrasion and wear. Cutter cone assemblies having machined cutting structures formed in accordance with teachings of the present invention may be used with rotary cone drill bits, core bits, hole openers, and other types of earth boring equipment.